The following abbreviations are herewith defined:    BB baseband    IC integrated circuit    IF intermediate frequency    LNA low noise amplifier    LO local oscillator    PLL phase lock loop    RF radio frequency    RX receiver    VCO voltage controlled oscillator    VDD power supply voltage
Presently, multi-band receivers that are implemented using ICs incorporate receiver front ends that include multiple off-chip filters. These multiple off-chip filters increase the size, complexity, power consumption and the assembly cost of multi-band transceivers and their use is generally undesirable.
It can be appreciated that those skilled in the art would desire a one-chip, multi-band receiver design. Such a one-chip multi-band receiver design would preferably not require multiple off-chip filters, including a particular filter (image rejection filter) that is typically positioned between the LNA and the frequency mixer. As is explained in commonly assigned US 2003/0176174 A1, “Method and Apparatus Providing Calibration Technique for RF Performance Tuning”, Pauli Seppinen, Aarno Parssinen, Mikael Gustafsson and Mika Makitalo (incorporated by reference herein in its entirety), the image rejection filter(s) are typically required due to leakage of transmitter power into the receiver input in full duplex systems, having a simultaneous transmission and reception mode (such as 3G CDMA systems).
However, the elimination of the off-chip filter between the LNA and the mixer requires that signal filtering be accomplished by other means. If the signal filtering is not performed, or is performed incorrectly, the mixer output signal will include an undesired signal component in addition to the desired signal component. This undesired signal component can, in a worst-case scenario, totally destroy the reception of the desired signal component(s).
Further, multi-band requirements for the receiver can alter the front end in such a way that a fixed filter can no longer be implemented between the LNA and mixer. This can occur because, typically, one set of controllable front-end components are used for each frequency band of interest. Thus, those skilled in the art would also desire a front-end design that accommodates multi-band operation without the complexity associated with providing filters for each frequency band.
More specifically, a portion of a receiver (the receiver “front end”) 100 according to the prior art is depicted in FIG. 1. In this particular example the receiver 100 operates in five frequency bands (Band_1 to Band_5). The receiver 100 includes filtering and impedance matching components 111 and 115 (referred to for simplicity as filters) that are connected to a wideband antenna 105. The filters 111 and 115 are in turn respectively connected to LNAs 121 and 125. The outputs of the LNAs 121 and 125 are in turn connected to image rejection filters 151, 153, . . . 155, respectively, and thence to mixers 131, 133, . . . , 135. Using the mixers 131-135 the signals are mixed down (downconverted) to baseband (e.g., zero Hertz, close to zero Hertz, or to any suitable IF when implementing a super heterodyne or equivalent receiver) for further signal processing. VCOs contained in PLL and calibration circuit blocks 141-145 are connected to mixers 131-135, respectively, and provide appropriate mixing frequency signals thereto. As is apparent from FIG. 1, separate calibration circuitry (part of the PLL and calibration blocks 141-145) is required for servicing the five frequency bands of interest. Note that Band_1 and Band_2 are serviced by the same PLL and calibration block 141 in this non-limiting example of the prior art.
The complexity of the prior art receiver design 100 is further increased by the need for off-chip image rejection filters 151-155. The effective circuit duplication, function overlap and need for chip interconnects to accommodate off-chip filtering processes results in a complex and costly receiver implementation.